In the past ten years the numbers of sport utility vehicles “SUV” and pickup trucks have increased dramatically to the point where those vehicles are more popular than the millions of passenger cars on the road. The SUV and trucks inherently have a higher center of gravity than normal passenger cars due to the need for higher ground clearance for bad weather travel (snow and ice), off-road use and/or for pickup truck payloads. Typically these vehicles have a higher center of gravity and so a greater propensity to sway or even rollover during abrupt lane changes and evasive steering maneuvers than the lower normal passenger cars.
One important arrangement of all these vehicles is the method of suspension used. Except for the use of hydraulic shock absorber damping resistance to rebound, all suspension have the vehicle chassis and body load supported on the vehicle axles with various types of springs that resist primarily load and jounce of each wheel axle. All existing coil springs, leaf springs, air springs, torsion bars or rubber blocks suspensions have no provision for control of the rebound forces of inertia and gravity negative suspension loads. Particularly, those rebound loads occurring at the inside wheel during hard cornering or if a wheel drops into a pot hole.
Typically, changes in suspension loads while driving straight along a road are caused generally by reactions to bumps, pot holes, and roughness encountered by the vehicle wheels during their interaction with the road surface. Thus the suspension springs and associated shock absorbers quell the harshness and movements being transmitted to the body and chassis.
The sway or side to side rolling motions that vehicles experience due to cornering forces, also cause vehicle springs to be loaded or unloaded, depending which way the vehicle is rolling during cornering. Many vehicles have an anti-sway/roll bar installed to help the vehicle body resist the rolling actions. These devices help somewhat the vehicle resist roll but only as it relates to the body lean, because they are fixed to the sprung mass and leaning with the body. Thus, they actually reduce the load on the unloaded side of the vehicle. They use the body as a structure to support the torsion bar of the anti sway system transferring wheel jounce motion across to the opposite side. The disclosure herein will obviate the need for anti-sway bars saving the cost of providing and installing them. Shock absorbers only dampen the bouncing movement of the vehicle wheels and suspension caused by the reaction to road surface, cornering and braking. Thus, the rate of sway may be affected to a minor degree.
The transitory effects of body roll during cornering compress the springs on the side of the vehicle following the outside of the turn due to increased transfer weight to that side. Meanwhile the springs on the side of the vehicle, following the inside of the turn, unload extending toward their free position using the axle as a location for inducing lift of the sprung weight on that side resulting in increased body roll. Roll or sway during sudden cornering or evasive maneuvers rotates the vehicle and its center of gravity “CG” around the Roll Center axis. The Roll Center axis is a function of the particular vehicles suspension geometry. Roll or sway is increased if the CG is raised as in a SUV, four-wheel drive vehicle or truck.
A sudden turn opposite the direction of vehicle travel can cause momentum to continue the sway of the vehicle forcing its CG to move laterally past its maximum upright position, and so the vehicle continues on rolling and overturns. U.S. Pat. No. 2,160,541 has a paired spring suspension connected in series to only support load and jounce with the added spring coupled in line with the main spring for increasing the effective spring constant at the extremes of suspension travel. The techniques disclosed in the various embodiments of '541 are in the nature of an overload spring that engages and changes the spring constant at the extremes of wheel travel. There is no spring in '541 connected to specifically resist rebound forces due to diverging motion of the sprung weight to unsprung weight. The disclosure of '541 specifically states that the higher spring constant results in less flex (on page 2 column 1 at lines 6 to 8), “ . . . which opposes any tendency of the vehicle to overturn laterally when negotiating a turn.” In each embodiment of '541 the springs act in unison to control primarily load and jounce and there is no teaching of a particular connection to directly apply rebound reaction of unsprung weight to one of the springs. The graph in '541 showing wheel travel verses spring forces verifies these conclusions. U.S. Pat. No. 5,263,695 discloses a refinement of the '541 teaching that includes a shock absorber for damping motion and an elastic block to ameliorate the transition between first and second springs for carrying the load. In addition to many disclosures in '695 of prior paired spring configurations there is a specific explanation in column 5, lines 1 through 5 as follows:
“The suspension according to the invention produces a comfort level which is higher the more the transition from one stiffness to the other takes place progressively (see the patents cited in the state of the art).”
The state of the art referred to includes prior patents of the same inventor and the acknowledgements of those prior patents clearly identifies the teachings as merely two springs of different stiffness in series. Even in FIG. 7 of '695 the springs are concentrically mounted but act in series, see column 4, lines 8 through 12. At best the structures for multiple springs shown in these patents have differing spring rates to give an allegedly more comfortable ride.
No existing suspension system suspends the chassis and/or body between opposing springs to counter load and jounce and reaction and rebound along different portions of the axle and wheel travel. An opposing spring suspension can have little effect on the ride stiffness but stabilizes cornering and evasive maneuvering sway by helping the vehicle to resist roll while maintaining the general ride quality.